Determine, using germfree and conventional rats, the metabolic activity of the colonic microflora to metabolize a wide variety of precarcinogens, carcinogens, and their metabolites, like 1,2-dimethylhydrazine, azoxymethane, methylazoxymethanol, 3,2'-dimethyl-4-aminobiphenyl, and 3-methyl-2-naphthylamine, and the metabolic capacity of the small intestinal and colonic mucosa to metabolize these compounds and their metabolites to the proximate and/or ultimate carcinogens. Incubate the radiolabelled compounds with the colonic contents, small intestinal and colonic mucosal fractions, and isolated small intestinal and colonic loops from the germfree and conventional rats and the metabolic products formed will be identified.